1. Field
The present invention relates generally to medical imaging systems, and more particularly to a method and apparatus for evaluating regurgitation of blood from heart valves.
2. Background
Regurgitation, or the backward flow of blood through a defective heart valve, is a critical measurement used quite extensively in cardiology. Ideally, all the blood that is passed from one chamber of the heart to another chamber gets pumped out by the second chamber. Valves in the heart should prevent the flow of blood from a succeeding chamber back to a preceding chamber. For example, a mitral valve between the left atrium chamber of the heart stops flow back into the left ventricle chamber of the heart. However, in some diseased hearts, the valves operation might not be optimal. In such cases some amount of regurgitation, or back-flow, exists from a higher pressure succeeding chamber to a lower pressure preceding chamber.
Ultrasound devices have been developed and refined for the diagnosis and treatment of various medical conditions. Such devises have been developed, for example, to track the magnitude and direction of moving objects, or the position of moving objects over time. By way of example, Doppler echocardiography is one ultrasound technique that is used to determine information about the motion of blood and tissue for the diagnosis and treatment of cardiac conditions. In echocardiography the motion information is obtained from recordings and measurements of Doppler data.
The Doppler principle, as used in Doppler echocardiography, is well known and generally involves exploiting an observed phenomenon that the frequency of reflected ultrasound pulses is altered by a moving object, such as moving tissue or blood cells. This alteration, or change, in frequency is generally referred to as a Doppler shift, with the magnitude of the frequency change, or Doppler shift, being related to the velocity of the moving object form which the ultrasound pulses are reflected. The polarity of the frequency change, or Doppler shift, is related to the direction of motion relative to the ultrasound source: a positive frequency shift (increase) indicates the motion is towards the ultrasound sensor and a negative frequency shift (decrease) indicates that the motion is away from the ultrasound sensor. As such, the magnitude and polarity of the Doppler shift can be used to track the magnitude and direction of moving objects.
Intra-cardiac ultrasonic imaging, a technique where a steerable catheter fitted with an ultrasound transducer on its tip is used to view the interior anatomy of a beating heart has significantly improved the definition and clarity of views of diseased valves. However, a drawback to intra-cardiac ultrasound imaging is the need to account for a field of view which is constantly in motion. Furthermore, given the dynamics of an interventional cardiology procedure, where intra-cardiac ultrasound is predominantly employed, an imaging catheter could also be in constant motion due to blood flow. This can cause measurements difficulties, due to the dynamic qualities involved, such as the dynamics of the field of view and the catheter. In addition, the position of the ultrasound imaging head, or transducer, can be restricted to fields of view where the blood flow across a valve being studied is close to orthogonal to the ultrasound beam, where existing Doppler techniques have difficulty operating. It is also desirable, in many cases, to assign a quantitative value, or number, to regurgitation measurements and associated abnormal flow patterns, including turbulence.
Thus, a need exists for improved measurement and quantification of heart valve regurgitation.